The question is perhaps based on an Islamic spin on a midrash, as we can see from Ali's recently changed link, though I think one can say the same thing about the Islamic story as about the midrash.
This was polemics, not "sneakiness". Consider the midrash:
Terah was an idol manufacturer who once went away and left Abraham in charge of the store. A man walked in and wished to buy an idol. Abraham asked him how old he was and the man responded “fifty years old.” Abraham then said, “You are fifty years old and would worship a day old statue!” At this point the man left ashamed.
Later, a woman walked in to the store and wanted to make an offering to the idols. So Abraham took a stick, smashed the idols and placed the stick in the hand of the largest idol. When Terah returned he asked Abraham what happened to all the idols. Abraham told him that a woman came in to make an offering to the idols. Then the idols argued about which one should eat the offering first. Then the largest idol took the stick and smashed the other idols.
Terah responded by saying that they are only statues and have no knowledge. Whereupon Abraham responded by saying that you deny their knowledge, yet you worship them! At which point Terah took Abraham to Nimrod.
Nimrod proclaims to Abraham that we should worship fire. Abraham responds that water puts out fire. So Nimrod declares they worship water. Abraham responds that clouds hold water.
So Nimrod declares they worship clouds. Abraham responds that wind pushes clouds. So Nimrod declares they worship wind. Abraham responds that people withstand wind.
Nimrod becomes angry with Abraham and declares that Abraham shall be cast into the fire, and Abraham is correct that there is a real God, that God will save him. Then Abraham is cast into the fire and is saved by God.
Abraham’s brother Haran sees what happened and says that he believes in the God of Abraham, is thrown into the fire, and is not saved by God. Hence the verse in Genesis 11:28 “And Haran died in the presence of his father Terah in the land of his nativity, in Ur of the Chaldees.”
If one is sensitive to nuances in the text, then I think it becomes obvious that the genre is not (necessarily) history but polemics. Avraham, as the first official monotheist, gets to put forth all sorts of arguments against idolatry (which in this case is fetishism, that the idol itself has power, rather than the belief that the idol is a representative of the power on high).
Avraham in this story is not sneaky at all. He knows full well what Terach will respond, that
they are only statues and have no knowledge
Neither Avraham nor Terach are idiots. Avraham was not trying to destroy the idols while offering a fake excuse. Avraham was trying to prompt this very response from Terach, so that he could say the punch line of the polemic:
you deny their knowledge, yet you worship them!
This then matches the earlier polemic in the midrash, that the man is older than the idol, yet he would worship it.
It would have been "sneaky" had Avraham thought that he would get away with the deed with this excuse. But that would be a misreading of the midrash.